45 2 Of the Propagation of Heat 



experiments, which I think throw more light upon it, 

 and which will consequently render the investigation 

 easier and more satisfactory. 



With a view to determine how far the power which 

 certain bodies appear to possess of confining Heat, 

 when made use of as covering, depends upon the natures 

 of those bodies, considered as chymical substances, or 

 upon the chymical principles of which they are com- 

 posed, I made the following experiments. 



As charcoal is supposed to be composed almost en- 

 tirely of phlogiston, I thought that, if that principle 

 was the cause either of the conducting power or the 

 non-conducting power of the bodies which contain it, I 

 should discover it by making the experiment with char- 

 coal, as I had done with various other bodies. Accord- 

 ingly, having filled' the globe of the passage-thermometer 

 with 176 grains of that substance in very fine powder 

 (it having been pounded in a mortar, and sifted through 

 a fine sieve), the bulb of the thermometer being sur- 

 rounded by this powder, the instrument was heated in 

 boiling water, and being afterwards plunged into a mix- 

 ture of pounded ice and water, the times of cooling were 

 observed as mentioned in the following table. I after- 

 wards repeated the experiment with lampblack, and with 

 very pure and very dry wood-ashes ; the results of which 

 experiments were as under mentioned : 



